Spray adjuvants. 28

What are spray tank adjuvants?

Spray tank adjuvants are compounds that are added to a tank mix to aid a chemical’s mixing, application, or how well it works. Agricultural spray adjuvants include specialty adjuvants like tank buffers, anti-drift agents, anti foam products and spray stickers. Some spray adjuvants are already included in the formulation such as (Rapid Fire® – Glyphosate) or they may be products that are added to a tank mix. The use of spray adjuvants has become increasingly common in Sydney and Canberra due to the unique climates that turf managers face.

Spray adjuvants are in use regularly in the turf industry with for example, Duke® herbicide, a sulfonylurea herbicide recommending to use a non ionic surfactant to get the best results. At the end of this article is a list of pesticide adjuvants to use with turf products. Information on soil adjuvants and our recent blog on Hydroforce Ultra are in other sections. For more detailed information on what adjuvants you should use with which turf chemical see the Turf Chemical Guide.

Do spray tank adjuvants work?

The simple answer is yes but only if you use the right one. I’m going to use quinclorac which is the active in Quinstar to show what I mean. 

Zawierucha in 1998: 

• Quinclorac applied without an adjuvant failed to provide control of sowthistle;
• All adjuvants increase quinclorac activity except for a modified polysiloxane;

Woznica, Z et al 2003 looking at how well quinclorac works when mixed with nonionic surfactants, methylated seed oil (MSO), spray pH, and salts present in spray carrier. 

• Quinclorac works nearly twice as well on green foxtail when the spray mixture pH is increased from 2.6 to 7.3.

The benefits of spray tank adjuvants:

• First, they help with product mixing;
• Second, they give better herbicide contact with plant tissue and so better spray coverage;
• Third, they increase rates of chemical movement through the leaves and stomata;
• They increase the safety of a chemical by increasing its selectivity; and
• Adjuvants can also reduce the rate of a chemical by up to 5-10 times and so reduce costs. Adjuvants cost a lot less than turf chemicals and a USA study shows that using these can result in a 40% reduction in costs. Hence, using an adjuvant will in many cases improve how well a turf chemical works although in some situations adding adjuvants will not improve control. The graph below shows how adding a spray tank adjuvant improves the performance of azoxystrobin.

Thanks to the USDA Agricultural Research Service for these videos. They clearly demonstrate how using the right spray tank adjuvant can improve movement into a leaf.

The negatives of using spray adjuvants.

Spray tank adjuvants can also have negative effects. Firstly, they can reduce how well a chemical works. Besides this they can also increase the life of chemicals or even be dangerous themselves. This is the case with the carrier in many glyphosate formulations. In fact there is no perfect adjuvant that makes all turf chemicals perform better in all situations.

History of spray tank adjuvants.

In January 2013 the APVMA released data for chemical use by dollar value. You can see the 2020-21 figures below. In short, both the number and the value of adjuvant sales have shown huge increases. When these were first introduced despite having little supporting data some pretty big efficacy claims were made. At first they were simple soaps, as well as vegetable, and petroleum-based oils. As a result of a significant amount of investment there have been major advances in discovering how these work, as well as the results from using them.

Using spray adjuvants to get better results.

Spray adjuvants have several modes of action. The most important of these are the retention, spreading, and movement of chemicals into plants coupled with their ability to effect the droplet size. There are three classes on the market.

Activator spray tank adjuvants

These improve the performance of a chemical by for example increasing chemical ingestion. Surfactants, crop oils, crop oil concentrates (COCs), vegetable oils, methylated seed oils (MSOs), petroleum oils, nitrogen fertilizers, and silicone derivatives, all fall in this class.

Spray modifiers.

Spray modifiers include spray stickers, spreaders, and drift control agents and change the physical nature of a spray solution.

Utility spray tank adjuvants

Ultility adjuvants include products like anti foam, spray buffers, and water conditioners and increase the range of conditions where you can use a turf chemical.

Surfactants

These are the most common group of spray adjuvants. Surfactants comes from SURFace ACTive ageNTS and they reduce a spray solutions surface tension and how it behaves. By lowering the surface tension this means that the product spreads out and covers the leaf rather than beading up on the surface.

The surface tension of water is 72 dynes/cm, and using surfactants will in fact reduce the surface tension of a spray down to 20-30 dynes/cm. This reduction in surface tension allows more uptake as the spray stays in contact with the leaf surface for longer.

Examples of non ionic surfactants include EO-PO Block copolymers, organo-silicones, and alkylpolyglucosides (APG).

They can also influence uptake by changing the viscosity and structure of leaf and stem waxes, therefore making it easier for a herbicide to enter the plant.

Surfactants work by:

• Allowing more uniform spreading over the leaf surface. For example, they act as wetting agents for herbicide sprays;
• Increasing the sticking of a spray on the target plant;
• Increasing movement past leaf hairs etc;
• Preventing spray deposit crystallization and
• Increasing drying time and water retention of a spray.

In fact environmental conditions, the nature of the target plant as well as any interactions between the surfactant and a chemical will all affect the result of a spray. The balance between the hydrophilic (water-soluble) and lipophilic (oil soluble) components is called the Hydrophillic –Lipophilic Balance (HLB). When you use a spray adjuvant it is best to use a lipophilic adjuvant with a lipophilic chemical and vice versa. e.g. oil soluble herbicides work best with surfactants that have an HLB of 1 to 10 while water soluble herbicides work best with surfactants with an HLB of 10 to 20.

Table showing HLB range for spray adjuvants

The three main types of surfactants are nonionic (no charge), anionic (negative charge), and cationic surfactants (positive charge). Both anionic and cationic surfactants are not often used on turf.

Nonionic Surfactants as spray tank adjuvants

Nonionic surfactants are the most common of these. As well as being hydrophilic (water-loving) due to having no ionic charge they do not have a negative effect on a spray mix. All products termed spray wetters, spray spreaders, and organosiloxanes are in this class. Nonionic surfactants reduce the surface tension of a spray solution and also change the nature of a leaf surface by impacting the leaf cuticle.

Organosiloxanes (Proforce Scrubwet®) also reduce the surface tension of a solution, form a thin layer on the leaf surface. Due to their unique properties, spray solutions move through the stomata and they also influence the amount of chemical that passes through the cuticle. Owing to this super spreading property it also makes them nearly impossible to wash off a leaf surface even if it rains after being applied.

Work shows that an organosilicone adjuvant significantly improves the uptake of phosphorous acid into Pinus radiata needles and improves its performance against Phytophthora species. Ongoing work is looking at using these to help with the control of adult stem weevil.

Oils

The three types of oil-based adjuvants are crop oils, crop oil concentrates, and also methylated seed oils. They are popular, because they increase the movement of a chemical spray into a plant and help reduce surface tension.

Crop Oils

These are also known as petroleum oils and do not contain vegetable oil, and also contain a maximum of 5% surfactant. Crop oils promote the movement of a chemical spray either through a plant’s waxy cuticle or an insect’s tough, chitinous shell. Traditional crop oils are more commonly used for insect and disease control and seldom with herbicides.

Crop Oil Concentrates (COCs)

These contain 10-20% non-ionic surfactant. COC’s are also known as penetrating agents and also as excellent spreading agents. As they help make some of the less-soluble herbicides more soluble in water they are often used with grass herbicides. Good examples of these are Hasten spray adjuvant and Banjo spray adjuvant which are a combination of vegetable oil and nonionic surfactant.

Methylated seed Oils (MSOs)

These are oil-based surfactants and and take care when using these as they can cause leaf burn and phytotoxicity. In fact these are the most active of the activator adjuvants, working best on larger or drought-stressed weeds that are not growing. These have the following benefits:

• They increase the drying time on a leaf surface and as a result increase the potential for herbicide uptake;
• They can also improve chemical penetration of a leaf by solubilizing waxes;
• You get better control of larger weeds;
• You get better control of stressed weeds that are not growing and
• They work well on difficult-to-control weeds.

There are several reports of MSO’s improving the performance of quinclorac for controlling spurge or summergrass. This happens because using an MSO with quinclorac enhances the chemical movement into the leaf and maintains it in solution rather than it being able to crystalize on the leaf surface.

Use of Nominee for winter grass control shows that treatments with an MSO spray adjuvant and a nonionic surfactant, need 25 and 41% lower rates, compared to the normal rates without using adjuvants.

Tank buffers

For the most part the ideal water pH for most turf chemicals is in the range of 4.0 to 6.5, and it is best between 5.5 to 6.5. One outlier to this are the Group 2 herbicides, which give better results at a pH of 7 or greater. The reason why most chemicals work better in the 4-6.5 pH range is due to what is called alkaline hydrolysis.

In brief, above a pH of 7 some turf chemicals tend to be prone to this such as iprodione-based fungicides like Voltar® 500SC. This has a half-life of 48 minutes at pH 7. Using a tank buffer such as Manta Ray® lowers the pH of the water in the spray tank and so helps maintain the pH at a constant level. The end result is fewer re-sprays, more consistent performance, and reduced chemical usage and labour costs. 

Water pH

If you think water pH doesn’t effect you think again and be aware water quality changes throughout the year so it needs regular checking. Generally speaking tap water in Australia is artificially increased to above pH 7. So if you use this as your spray tank water in some cases you will need to use a buffer. Do not however, get into the habit of using a buffer in every tank mix. For example at a low pH 2,4-D amine tends to drop out of solution or form a gel.

As a start if you don’t have a current water analysis and your using town water Tthere are some great online water analysis tools depending on where you are. Simply fill in your post code and it will give you a water analysis.

Sydney Water quality

Melbourne Water quality

South East Melbourne Water quality

South East Queensland Water quality

Canberra Water quality

Table showing spray tank stability.

Anti-foam

Anti-foam reduces foam build up which is an issue in soft water areas like the ACT. Polydimethylsiloxane is the active ingredient in Foam-aid® and is unique because not only does it prevent foaming while mixing or spraying but also can remove foam that is already present.

Deposition and Drift Control Agents

Deposition aids are also called spray stickers since they increase how long a chemical lasts once applied to a leaf surface. Other properties include an ability to reduce evaporation and also an increase in UV stability. Bond adjuvant® or Octane® are examples of these.

Drift control agents reduce spray drift by increasing the size of spray droplets. As droplets with a diameter of 150 microns or smaller will tend to drift, the use of drift control agents means you can better target your spray. This is due to the fact that they increase the average droplet size and they achieve this by binding with water molecules to form larger spray droplets.The best of these appear to be products based on guar gum.

Since 2010 there has been a law to assess new chemicals for the potential risk of spray drift. As a result of this no spray buffer zones are now listed on labels of products like Specticle herbicide® and Numchuk Quad®.

Modifying spray droplet size.

By and large wetting agents reduce the spray drop size while oil-based adjuvants tend to increase the drop size. When spraying, consider the nozzle selection, operating pressure, boom height, and also the prevailing weather conditions.

For the most part don’t rely solely on these for dealing with off-target drift. Water-based sprays are the standard means of applying chemical sprays in the turf industry, and the aim is to use a specific-sized spray to get the best results. Drift occurs if droplets are too small. In contrast, if drops are too large they will tend to run off the target.

Foam Markers and Colourants

Foam markers are spray adjuvants that are used to see where you have sprayed without having to use a colourant. This helps avoid overlap when applying turf chemicals. Colourants such as Blue spray indicator are used as marker or indicator dyes to identify areas that have already been sprayed. This is in contrast to turf pigments that are used as broad acre masking agents and also to stimulate growth.

Spray Tank Cleaners

Spray tank cleaners remove nasty residues that can be left after spraying. Tank cleaners are often based on sodium tripolyphosphate and these should always be used to clean a spray tank if it has been used with non selective herbicides like glyphosate.

Ammonium Fertilizers

Urea-ammonium nitrates (UAN), and ammonium sulphate (AMS) are all used as spray tank adjuvants to reduce the negative effects of hard water ions. These include Fe, Zn, Mg, Na, K, and calcium and can react with some herbicides such as 2,4-D and glyphosate to form insoluble precipitates.

In fact in areas with hard water, you should consider always using crystalline or spray-grade ammonium sulphate to stop the calcium form of glyphosate forming. Although tempting, don’t use granular or standard ammonium sulphate with glyphosate as these both contain impurities that will give poor results.

Also if you add crystalline ammonium sulphate to a spray tank the temperature of the spray solution will drop which is an endothermic reaction. Because of this be aware that in winter the drop in temperature can make the mixing of turf chemicals into the spray tank difficult. For this reason fill the tank at least three-quarters full before adding crystalline ammonium sulphate.

Our chemical and irrigation suitability water analysis calculates exactly how much ammonium sulphate you need.

Table showing rate of ammomium sulphate for hard water.

Turf is very good at taking up NH4 ions and this is because when it does it is at the expense of H+ ions which are transferred to the outside of cells. The result of this, is a drop in the pH. By using NH4 in a spray tank it increases herbicide uptake by creating a pH gradient across cell membranes.

Map of hard water areas in Australia

Compatibility Agents

How often do you want to know if you can mix some ingredients and if they are compatible? Compatibility agents are added to spray tanks to avoid chemical mixing issues by preventing antagonism between ingredients. For example, the spray adjuvant Fix-it Tank Mix® does this. Here is a method for a  “jar test” to find out the stability of a mixture. Always remember to wear personal protective equipment (PPE) when handling turf chemicals

To do this you will need a 1L or bigger glass jar. The key point to note is that how well a tank mix works depends on how well the products mix in a spray tank.

How to carry out a Jar Test.

Step 1. Measure 500ml of water into the glass jar. You want to use the same water source you are going to use in the spray tank.

Step 2. You are trying to mirror on a small scale what happens in your spray tank. Add the products you want to use in the same amounts, one at a time, as per the label. If the order for adding turf chemicals is not listed on the label add them in the following order. Each time a product is added make sure you stir it well until the next one is added. For example, add emulsifiable concentrates before liquid UAN, etc.

• First, add your compatibility, buffering, or defoaming agents;
• Second add wettable powders, dry flowables, water-dispersible granules;
• Third, add flowables, liquids, microencapsulated products;
• Next add, solutions, soluble powders;
• Then add the remaining adjuvants, such as surfactants or crop oils;
• Then add any emulsifiable concentrates; and finally add
• Liquid UAN

Step 3. Shake the jar and leave it for at least 15 minutes. The mixture is not compatible if a scum forms on the surface, or the mixture separates, solids form and settle to the bottom, or clumps or gels form. Also look for other signs of a reaction, such as heat or a smell. If the jar feels warm to the touch and/or there is a strong smell don’t use the mixture. If issues occur, this mix is not compatible and should be thrown away.

How to choose the right spray tank adjuvants

• First, make sure you read the product label as this is there for a reason. Many product labels list what adjuvant to use and in some cases the label may have these details under the “Directions for Use” section;
• Second, use the active ingredient content to calculate the actual cost;
• Third, use a reputable brand with supporting data. Do not use anything other than a formulated adjuvant as it may impact on the chemical performance. So for those that use washing up liquid. Stop!
• Next, if it makes claims that sound to good to be true, they are!
• You don’t always have to add an adjuvant and
• Make sure that your equipment is set up properly.

Spray adjuvant list for commonly used turf products

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